1. Field of the Invention
The present invention relates to a magnetooptical recording medium on which information is recorded, and from which information is reproduced, and erased using a laser beam, and a magnetooptical recording/reproduction method.
2. Related Background Art
A conventional magnetooptical recording method is time-consuming since it requires three processes, i.e., erasing, recording, and collation processes to be performed upon the recording of information. In order to solve this problem, the following overwrite methods have been proposed.
1 Magnetic Field Modulation Method
In this method, the intensity of an irradiation laser beam is maintained constant, and the polarity of a magnetic field to be applied is inverted at a high speed in correspondence with recording information, thereby achieving recording (Japanese Laid-Open Patent Application Nos. 63-204532 and 63-76135, and the like). In this method, the polarity of the magnetic field to be applied must be inverted at a high speed. For this reason, high electric power must be input in order to generate a recording magnetic field from a position separated from the medium surface by a given distance so as to prevent collision between a recording head for generating the magnetic field and the medium surface, and it is technically difficult to realize this method. Also, a method of bringing a magnetic head very close to the medium surface is proposed. However, with this method, the original advantage of an optical disk, i.e., non-contact recording/reproduction, is not utilized.
2 Exchange-coupled Two-layered Film Method
In this method, a magnetooptical recording medium which comprises, as a recording layer, a two-layered film consisting of a rare earth-transition metal amorphous alloy, is used, and an overwrite operation is performed by utilizing the exchange-coupling force between the two layers (Japanese Laid-Open Patent Application No. 62-175948, and the like). More specifically, a magnetooptical medium, which comprises a recording layer consisting of, e.g., TbFe, and an auxiliary layer consisting of TbFeCo, is used. After initialization for aligning the direction of magnetization of the auxiliary layer is performed, a recording bias magnetic field is applied, and a laser beam of binary power irradiates the medium, thus realizing an overwrite operation. With this method, there is a case of providing a magnetic wall between the two layers when information is recorded, and a problem associated with stability of recorded information, a problem associated with a large magnetic field required in initialization, and the like still remain unsolved.